In recent years, the sizes and thicknesses of appliances are being reduced with progress in the field of electronics. As a result, various pressure-sensitive adhesives for use in such appliances have come to be required to have various properties. In particular, there is a growing desire for heat resistance. This is because the size and thickness reductions in appliances have resulted in considerable heat buildup. Although various measures for removing generated heat are being investigated, various pressure-sensitive adhesives are required to have further improved heat resistance.
Silicone pressure-sensitive adhesives have excellent heat resistance. However, the silicone pressure-sensitive adhesives are highly expensive and are unsuitable for general applications. Consequently, the heat resistance of inexpensive acrylic pressure-sensitive adhesives is expected to be improved.
Acrylic pressure-sensitive adhesives have excellent transparency, and the pressure-sensitive adhesive properties thereof can be easily controlled by changing the composition of the constituent monomers. Acrylic pressure-sensitive adhesives hence have conventionally been applied to many pressure-sensitive adhesive products and other adhesive products.
With respect to investigations for improving the heat resistance of acrylic pressure-sensitive adhesives, a technique in which an alicyclic acrylic monomer is introduced has been proposed (for example, patent document 1). Although this technique attains excellent pressure-sensitive adhesiveness to nonpolar substrates such as polyolefins, the technique is not so effective in improving heat resistance.
Furthermore, a technique in which an acrylamide monomer or the like is copolymerized to improve heat resistance has been proposed (for example, patent document 2). Although this technique brings about excellent reworkability, the pressure-sensitive adhesive has a heat resistance temperature of about 120° C. at most and has insufficient heat resistance in the field of electronics.    Patent Document 1: JP-A-2008-133408    Patent Document 2: JP-A-2008-308548